Our invention comprises an internal muffler for air conditioning compressors that is adapted to attenuate pressure pulsations. It comprises an improvement in known automotive air conditioning compressors such as those shown in U.S. Pat. Nos. 3,864,801 and 4,070,136.
Prior art compressor designs often comprise cast aluminum cylinder bodies in which are formed axially disposed cylinders, the cylinders of one cylinder body being axially aligned with respect to the cylinders of the other body. Reciprocating pistons are located within the cylinders, and the pistons are actuated by a swashplate adapted to be driven by a swashplate driveshaft.
As the swashplate rotates, the pistons, which slidably engage with swashplate, are reciprocated thereby establishing a pumping action. Compressor inlet and outlet valves are located at each axial end of the compressor assembly to accommodate the flow of low pressure refrigerant into the cylinders and the flow of high pressure refrigerant from the cylinders to a high pressure outlet. In prior art designs it is common practice, as illustrated in the patents identified above, for the housing to be formed with a crossover passage that connects each axial end of the compressor assembly with a centrally disposed discharge port, the latter extending radially with respect to the axis of the compressor. A cavity is formed in the housing parts so that the housing is capable of acting as a plenum chamber, and pressure pulsations that are developed at the flow exit sides of the cylinders for each housing portion are transferred axially toward the outlet. The pulsations of one high pressure passage generally interfere with and neutralize the pulsations acting in the other housing portion so that they tend to cancel each other.
The pulsation damping that is achieved in an arrangement of this type is unpredicable and there is no practical way of varying the length of the discharge passages through which the pulsations travel. Because of this the pulsations are perceived as an undesirable compressor noise sometime referred to as noise, vibration and harshness (NVH).